drm/atomic-helper: roll out commit synchronization

To facilitate easier reviewing this is split out from the overall
nonblocking commit rework. It just rolls out the helper functions
and uses them in the main drm_atomic_helper_commit() function
to make it clear where in the flow they're used.

The next patch will actually split drm_atomic_helper_commit() into
2 pieces, with the tail being run asynchronously from a worker.

v2: Improve kerneldocs (Maarten).

v3: Don't convert ERESTARTSYS to EINTR (Maarten). Also don't fail if
the wait succeed in stall_check - we need to convert that case (it
returns the remaining jiffies) to 0 for success.

v4: Switch to long for wait_for_completion_timeout return value
everywhere (Maarten).

v5: Fix miscaped function in kerneldoc (Maarten).
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Tested-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Tomeu Vizoso <tomeu.vizoso@gmail.com>
Cc: Daniel Stone <daniels@collabora.com>
Tested-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465398936-22305-1-git-send-email-daniel.vetter@ffwll.ch

include/drm/drm_atomic_helper.h

@@ -74,6 +74,13 @@ void drm_atomic_helper_disable_planes_on_crtc(struct drm_crtc *crtc,
 void drm_atomic_helper_swap_state(struct drm_atomic_state *state,
 				  bool stall);
 
+/* nonblocking commit helpers */
+int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
+				   bool nonblock);
+void drm_atomic_helper_wait_for_dependencies(struct drm_atomic_state *state);
+void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *state);
+void drm_atomic_helper_commit_cleanup_done(struct drm_atomic_state *state);
+
 /* implementations for legacy interfaces */
 int drm_atomic_helper_update_plane(struct drm_plane *plane,
 				   struct drm_crtc *crtc,